This invention relates to expansion joints for structures that carry vehicular traffic. The invention has been devised primarily in the environment of parking structures but may find application in other similar structures, for example, bridges.
Parking structures typically are constructed using reinforced concrete slabs to provide a traffic surface. The individual slabs are sized and spaced from one another to allow for relative movement between the slabs, in particular to accommodate expansion and contraction due to temperature changes. In some geographic areas, it is also necessary to accommodate relative movement caused by seismic events.
Expansion joints are used to cover the gaps between the slabs and prevent infiltration of moisture and debris. In a parking structure, the expansion joints must also be designed to withstand repeated cyclical movement caused by vehicles travelling over the joints. An expansion joint in a high-traffic area such as an entrance or exit ramp must be designed to withstand millions of cycles over its lifetime.
Another criterion is the ability to withstand lateral shear forces as vehicles move over the joints, and in particular lateral forces imposed on the joints when vehicles brake and/or accelerate with their wheels on the expansion joint.
In an effort to address these criteria, many different expansion joint designs have evolved, ranging from elastomeric seals that attempt to fill the gap, to cover plates that extend over and cover the gap. Typically, a cover plate is located in shallow recesses that are formed in the respective slabs on opposite sides of the gap so that the top surface of the cover plate is generally flush with the top surfaces of the slabs. The cover plate overlies a pair of rails that are bolted to the slabs in the respective recesses. A trough or water stop is provided in the gap below the cover plate to catch any moisture that might penetrate between the cover plate and the rails.
The cover plate is self-centering with respect to the gap by virtue of a series of turnbars that are pivotally coupled to the underside of the plate and engaged at their ends in slots that extend longitudinally of the rails. As the slabs move with respect to one another, changing the width of the gap, the turnbars angle more or less acutely with respect to the walls of the gap, maintaining the cover plate centred.
A drawback to this type of joint is that it is relatively vulnerable to lateral loadings, for example, when a vehicle brakes or accelerates with its wheels on the cover plate. Pivot pins or bolts coupling the turnbars to the cover plate may bend or even shear off.
Another weakness of this type of expansion joint is vulnerability to water infiltration around the rails that are mounted on opposing faces of the slabs. Typically, each rail is an extrusion that is bolted in place in a recess in the relevant slab. The extrusion is then xe2x80x9cback filledxe2x80x9d with elastomeric concrete which bonds to the extrusion and to the slab and is intended to seal out moisture. A difficulty with some expansion joints is that the extrusions have profiles that include undercut areas or xe2x80x9cpocketsxe2x80x9d that can be difficult to fill with elastomeric concrete. Concrete is a highly viscous liquid that is poured into place and allowed to set. The highly viscous nature of the material makes it difficult to ensure that undercut recesses in the extrusion are completely filled. If they are not, the elastomeric concrete may tend to shrink or pull away from the extrusion and/or slab, creating areas for water infiltration.
An object of the present invention is to provide improvements in expansion joints intended to address at least some of these drawbacks.
According to one aspect of the invention there is provided an expansion joint for installation across a gap between adjacent slabs of a structure intended to carry vehicular traffic. The joint includes first and second rails for mounting on the respective slabs at opposite sides of the gap and a cover plate dimensioned to overlie the respective rails and cover the gap while permitting relative movement between slabs. A plurality of turnbars are carried by the cover plate and coupled to the respective rails for maintaining the cover plate centered over the gap. Each turnbar has end portions that are coupled to the respective rails for sliding movement longitudinally of the rails in response to relative lateral movement of the slabs. Each turnbar also defines a pivot axis between its ends about which the turnbar turns with respect to the cover plate in response to lateral movement of the slabs. Each turnbar is connected to the cover plate by coupling means that includes socket on one of the turnbar and cover plate and the rotational coupling element on the other. The coupling element and socket are complimentarily shaped to allow turning of the turnbar with respect to the cover plate about the said axis while transferring lateral loads imposed on the cover plate in use directly to the turnbar and into the relevant slab via the rail mounted on the slab.
Preferably, the coupling between each turnbar and the cover plate is a ball and socket coupling so that the cover plate and turnbar can also tip to some extent with respect to one another. On the other hand, in applications in which tipping is unlikely to occur, the coupling element could, for example, be of cylindrical form. Most importantly, the coupling should provide a solid connection between the cover plate and turnbar so that lateral loads imposed on the cover plate are transferred directly to the turnbar and any propensity for the cover plate to move laterally with respect to the turnbars is minimized.
Preferably, the end portions of each turnbar are provided by formations that are enlarged with respect to the main, elongate body of the bar that extends between the end portions. The formations preferably are in line with that main body of the bar so that forces imposed on the bar are transmitted directly to the enlarged end portions. The rails in turn preferably define undercut slots that are complimentary to the profile of the enlarged end portions of the bar and that relatively closely accommodate those formations so that there is minimum free play between the bar and the rails. Again, the objective should be to transfer directly to the rails and, from there to the slabs lateral forces that are imposed on the plates and transferred from there to the turnbars. There should be minimal free play between these components.
Another aspect of the invention relates to the profile shape of the rail of the expansion joint.